For open deluge foam systems, foam concentration verification is conducted at which flow rate?

• A. The minimum design flow rate
• B. The maximum possible discharge
• C. Midrange design flow rate
• D. Actual calculated discharge demand

Answer: (C)

The main idea here is to verify foam concentrate concentration at a flow that represents typical operating conditions, not at the system’s extremes. For open deluge foam systems, the way the foam concentrate is metered and mixed is most accurately checked when the flow is around the design “midrange” level. At this rate, the proportioning device and mixing process are operating under normal conditions, so the measured concentrate closely reflects what would be delivered during a real fire.

Testing at the midrange design flow ensures the foam solution stays within the intended concentration across the normal portion of the system’s operating envelope. If you test at the minimum design flow, the flow may be too low for proper mixing and could overstate concentration issues. If you test at the maximum discharge, the flow could dilute the foam or excite dynamic effects that don’t represent typical operation. The calculated discharge demand varies with a fire scenario and isn’t a fixed test condition for verifying the system’s concentration.

So, midrange design flow rate is the best representative point to verify that the foam concentration meets design expectations across ordinary operating conditions.